Beam forming is based on the principle of adaptive antennas, which performs weighting processing on each antenna unit using an antenna array through advanced signal processing algorithms, so as to cause the array to align with a useful signal direction in real time, and form a zero point in an interference direction to suppress interference signals, thereby enhancing the signal to noise ratio, improving performance of a system and increasing coverage of the system, as shown in FIG. 1.
MIMO is a communication system in which multiple antennas are positioned in a transmitting end and a receiving end respectively. The MIMO can be mainly classified into two categories. When there are multiple antennas in the transmitting end or the receiving end and a data set transmitted by each transmitting antenna is the same, the receiving end combines the obtained signals from multiple branches, thereby improving the reliability of links. Such a MIMO technology is referred to as spatial diversity. In the case that there are two antennas in both the transmitting end and the receiving end, one of diversity coding modes is shown in FIG. 2(a), in which antenna 1 transmits symbols s1 and −s2* at two adjacent times (or sub-carriers) respectively, and antenna 2 transmits symbols s2 and s1* at two adjacent times (or sub-carriers) respectively. In addition, when there are multiple antennas at both the transmitting end and the receiving end, since a MIMO channel is equivalent to multiple parallel channels, multiple data streams can be transmitted in parallel simultaneously, thereby improving the data transfer rate. This is spatial multiplexing. In the case that there are two antennas in both the transmitting end and the receiving end, one of spatial multiplexing coding modes is shown in FIG. 2 (b), in which antenna 1 and antenna 2 transmit symbols s1 and s2 respectively on the same time-frequency resources.
MIMO is combined with beam forming to form a new technology with advantages of the two technologies, which is referred to as MIMO beam forming, or MIMO+BF for short. It can not only suppress interference signals, like beam forming, but also enhance the reliability or transfer rate of links, like MIMO. A structure of one of MIMO beam forming systems is shown in FIG. 3. The entire antenna array forms S beams, each of which being equivalent to a virtual antenna. A MIMO system is constituted between virtual antennas. The combination of beam forming with spatial diversity can be referred to as spatial diversity beam forming; and the combination of beam forming with spatial multiplexing can be referred to as spatial multiplexing beam forming.
Acquirement of weight values W for MIMO beam forming is one of key technologies of MIMO beam forming. Accuracy and timeliness of the weight values W significantly influences performance of the MIMO beam forming.